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	{{chembox		{{chembox
			|Verifiedfields = changed
⚫	| verifiedrevid = 398822350
			|Watchedfields = changed
	| ImageFile = crabtree.png
		⚫	|verifiedrevid = 439409758
⚫	| ImageSize = 220px
	| ImageName = Crabtree's catalyst		|ImageFile = Crabtree.svg
		⚫	|ImageSize = 220px
⚫	| ImageFile1 = Crabtree's-catalyst-cation-3D-sticks.png
			|ImageName = Crabtree's catalyst
	| IUPACName = (''SP''-4)tris(cyclohexyl)phosphane<br /><br />pyridineiridium(1+) hexafluoridophosphate(1−)
		⚫	|ImageFile1 = Crabtree's-catalyst-cation-3D-sticks.png
⚫	| Section1 = {{Chembox Identifiers
			|IUPACName = (''SP''-4)-(η<sup>2</sup>,η<sup>2</sup>-Cycloocta-1,5-diene)(pyridine)(tricyclohexylphosphane)iridium(1+) hexafluoridophosphate(1−)
⚫	| CASNo = 64536-78-3
		⚫	|Section1 = {{Chembox Identifiers
⚫	}}
			|CASNo_Ref = {{cascite|correct|??}}
⚫	| Section2 = {{Chembox Properties
		⚫	|CASNo = 64536-78-3
⚫	| Formula = C<sub>31</sub>H<sub>50</sub>F<sub>6</sub>IrNP<sub>2</sub>
			|UNII_Ref = {{fdacite|correct|FDA}}
⚫	| MolarMass = 804.9026 g/mol}}
			|UNII = 816RS2NBPN
			|PubChem = 5702647
			|ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
			|ChemSpiderID = 21170841
			|SMILES = c1ccncc1.C1CCC(CC1)P(C2CCCCC2)C3CCCCC3.C1/C=C\CC/C=C\C1.F(F)(F)(F)(F)F.
			|InChI = 1/C18H33P.C8H12.C5H5N.F6P.Ir/c1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2-4-6-8-7-5-3-1;1-2-4-6-5-3-1;1-7(2,3,4,5)6;/h16-18H,1-15H2;1-2,7-8H,3-6H2;1-5H;;/q;;;-1;+1/b;2-1-,8-7-;;;
			|InChIKey = UJXHUUQZACSUOG-KJWGIZLLBW
			|StdInChI_Ref = {{stdinchicite|changed|chemspider}}
			|StdInChI = 1S/C18H33P.C8H12.C5H5N.F6P.Ir/c1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2-4-6-8-7-5-3-1;1-2-4-6-5-3-1;1-7(2,3,4,5)6;/h16-18H,1-15H2;1-2,7-8H,3-6H2;1-5H;;/q;;;-1;+1/b;2-1-,8-7-;;;
			|StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
			|StdInChIKey = UJXHUUQZACSUOG-KJWGIZLLSA-N
	}}		}}
		⚫	|Section2 = {{Chembox Properties
⚫	'''Crabtree's catalyst''' is the name given to a ] of ] with ], tris-cyclohexylphosphine, and ]. It is a homogeneous catalyst for ] reactions, developed by ], a professor at ]. The iridium atom in the complex has a ], as expected for a d<sup>8</sup> complex.<ref>{{cite journal|author = ] | title = Iridium compounds in catalysis | journal = Acc. Chem. Res | year = 1979 | volume = 12 | pages = 331–337 | doi = 10.1021/ar50141a005|issue = 9}}</ref><ref>{{cite journal|author=Brown, J. M. |title = Directed Homogeneous Hydrogenation | journal = ] | date = 1987 | volume = 26 | pages = 190–203 | doi = 10.1002/anie.198701901|issue=3}}</ref>
		⚫	|Formula = C<sub>31</sub>H<sub>50</sub>F<sub>6</sub>IrNP<sub>2</sub>
			|Appearance = Yellow microcrystals
		⚫	|MolarMass = 804.9026&nbsp;g/mol
			|MeltingPtC = 150
			|MeltingPt_notes = (decomposes)<ref name="uses" />
		⚫	}}
			}}
		⚫	'''Crabtree's catalyst''' is an ] with the formula <nowiki>]Ir]]<nowiki>]</nowiki>PF<sub>6</sub>. It is a homogeneous catalyst for ] and hydrogen-transfer reactions, developed by ]. This air stable orange solid is commercially available and known for its directed hydrogenation to give trans stereoselectivity with respective of directing group.<ref name="original">{{cite journal|author= ]| title = Iridium compounds in catalysis | journal = Acc. Chem. Res. | year = 1979 | volume = 12 | pages = 331–337 | doi = 10.1021/ar50141a005|issue = 9}}</ref><ref>{{cite journal|last=Brown|first= J. M. |title = Directed Homogeneous Hydrogenation | journal = ] | date = 1987 | volume = 26 | pages = 190–203 | doi = 10.1002/anie.198701901|issue=3}}</ref>
			==Structure and synthesis==
⚫	Crabtree and graduate student George Morris discovered this catalyst in the 1970s while working on iridium analogues of ] ]-based catalyst at the ] at Gif-sur-Yvette, near Paris. One advantage of Crabtree's catalyst is that it is about 100 times more active than Wilkinson's and can hydrogenate even tri- and tetrasubstituted ]s.
			The complex has a ], as expected for a d<sup>8</sup> complex. It is prepared from ].<ref>{{cite journal|last1=Crabtree|first1=R. H.|last2=Morris|first2=G. E.|date=1977|title=Some diolefin complexes of Iridium(I) and a ''trans''-Influence Series for the Complexes |journal=J. Organomet. Chem.|volume=135|issue=3|pages=395–403|doi=10.1016/S0022-328X(00)88091-2}}</ref>
			==Reactivity==
	Crabtree's catalyst has also been used as the basis for the development of newer catalysts; by modifying the ligands, one can modulate the properties of the catalyst. For example, use of chiral ligands has led to the development of ] catalysts.
			Crabtree’s catalyst is effective for the hydrogenations of mono-, di-, tri-, and tetra-substituted substrates. Whereas Wilkinson’s catalyst and the Schrock–Osborn catalyst do not catalyze the hydrogenation of a tetrasubstituted olefin, Crabtree’s catalyst does so to at high turnover frequencies (table).<ref name = "original"/><ref>{{cite web|last=White|first=M.|date=2002-10-15|title=Hydrogenation|accessdate=2014-12-01|url=http://www.scs.illinois.edu/white/lectures/week5.pdf}}</ref>
			:{| class="wikitable"
	In the ] of a certain terpen-4-ol the comparison with traditional catalysts works out as follows.<ref>{{cite journal|title = Directing effects in homogeneous hydrogenation with PF6 | author = ] Davis, M. W. | journal = ] | date = 1986 | volume = 51 | issue = 14 | pages = 2655–2661|doi = 10.1021/jo00364a007}}</ref>
			|+Turnover frequencies
	With ] in ] the product distribution is 20:80 in favor of the ] ('''2B''' in ''scheme 1''). The polar side (with the hydroxyl group) interacts with the solvent leaving the apolar to the catalyst surface. In ] as ] the distribution changes to 53:47 where the polar side now has a slight preference for the catalyst. The distribution changes completely in favor of the cis isomer '''2A''' when Crabtree's catalyst is used in ]. This directing effect is due to a bonding interaction of the hydroxyl group with the iridium center. Carbonyl groups are also known to direct the hydrogenation by the Crabtree catalyst.
			! Substrate !! Wilkinson's catalyst !! Schrock–Osborn catalyst !! Crabtree's catalyst
			|-
			| Hex-1-ene || 650 || 4000 || 6400
			|-
			| Cyclohexene || 700 || 10 || 4500
			|-
			| 1-Methylcyclohexene || 13 || — || 3800
			|-
			| 2,3-Dimethyl-but-2-ene || — || — || 4000
			|}
			The catalyst is reactive at room temperature.<ref name ="uses">{{cite encyclopedia|last=Crabtree|first=R. H.|date=2001|title=(1,5-Cyclooctadiene)(tricyclohexylphosphine)(pyridine)iridium(I) Hexafluorophosphate|encyclopedia=e-EROS Encyclopedia of Reagents for Organic Synthesis|doi=10.1002/047084289X.rc290m.pub4|doi-broken-date=1 November 2024}}</ref> The reaction is robust without drying solvents or meticulous deoxygenation of the hydrogen. The catalyst is tolerant of weakly basic functional groups such as ester, but not alcohols (see below) or amines.<ref name = "original"/> The catalyst is sensitive to proton-bearing impurities.<ref>{{cite journal|last2=Mingos|first2=D. Michael P.|authorlink2=D. Michael P. Mingos|last3=Brown|first3=John M.|last1=Xu|first1=Yingjian|year=2008|title=Crabtree's catalyst revisited; Ligand effects on stability and durability|journal=]|volume=2008|issue=2|pages=199–201|doi=10.1039/b711979h|pmid=18092086}}</ref>
⚫	]
			The catalyst becomes irreversibly deactivated after about ten minutes at room temperature, signaled by appearance of yellow color. One deactivation process involves formation of hydride-bridged dimers.<ref>{{cite journal|last1=Crabtree|first1=R.|last2=Felkin|first2=H.|last3=Morris|first3=G.|date=1977|title=Cationic iridium diolefin complexes as alkene hydrogenation catalysts and the isolation of some related hydrido complexes|journal=]|volume=141|issue=2|pages=205–215|doi=10.1016/S0022-328X(00)92273-3}}</ref> As a consequence, Crabtree's Catalyst is usually used in very low catalyst loading.
			(cationic charge not shown).]]
			===Other catalytic functions: isotope exchange and isomerization===
			Besides hydrogenation, the catalyst catalyzes the isomerization and hydroboration of alkenes.<ref name="uses"/>
			]
			Crabtree's catalyst is used in ] exchange reactions. More specifically, it catalyzes the direct exchange of a hydrogen atom with its isotopes ] and ], without the use of an intermediate.<ref>{{cite journal|last=Schou|first=S.|date=2009|title=The effect of adding Crabtree's catalyst to rhodium black in direct hydrogen isotope exchange reactions|journal=Journal of Labelled Compounds and Radiopharmaceuticals|volume=52|issue=9|pages=376–381|doi=10.1002/jlcr.1612}}</ref> It has been shown that isotope exchange with Crabtree’s catalyst is highly regioselective.<ref>{{cite journal|last1=Valsborg|first1=J.|last2=Sorensen|first2=L.|last3=Foged|first3=C.|date=2001|title=Organoiridium catalysed hydrogen isotope exchange of benzamide derivatives|journal=Journal of Labelled Compounds and Radiopharmaceuticals|volume=44|issue=3|pages=209–214|doi=10.1002/jlcr.446}}</ref><ref>{{cite journal|last1=Hesk|first1=D.|last2=Das|first2=P.|last3=Evans|first3=B.|date=1995|title=Deuteration of acetanilides and other substituted aromatics using PF<sub>6</sub> as catalyst|journal=Journal of Labelled Compounds and Radiopharmaceuticals|volume=36|issue=5|pages=497–502|doi=10.1002/jlcr.2580360514}}</ref>
			===Influence of directing functional groups===
			The ] of a terpen-4-ol demonstrates the ability of compounds with directing groups (the –OH group) to undergo diastereoselective hydrogenation. With ] in ] the product distribution is 20:80 favoring the ] ('''2B''' in Scheme 1). The polar side (with the hydroxyl group) interacts with the solvent. This is due to slight haptophilicity, an effect in which a functional group binds to the surface of a heterogeneous catalyst and directs the reaction.<ref>{{cite journal|last1=Thompson|first1=H.|last2=Naipawer|first2=R.|date=1973|title=Stereochemical control of reductions. III. Approach to group haptophilicities|journal=]|volume=95|issue=19|pages=6379–6386|doi=10.1021/ja00800a036}}</ref><ref>{{cite web|last=Rowlands|first=G.|date=2002-01-01|title=Hydrogenation|accessdate=2014-12-01|url=http://www.massey.ac.nz/~gjrowlan/oxid/hydr.pdf|archive-date=2015-01-02|archive-url=https://web.archive.org/web/20150102053039/http://www.massey.ac.nz/~gjrowlan/oxid/hydr.pdf|url-status=dead}}</ref> In ] as ], the distribution changes to 53:47 because haptophilicity is no long present (there is no directing group on cyclohexane). The distribution changes completely in favor of the ''trans'' isomer '''2A''' when Crabtree's catalyst is used in ]. This selectivity is both predictable and practically useful.<ref>{{cite journal|last1=Brown|first1=J.|date=1987|title=Directed Homogeneous Hydrogenation |journal=]|volume=26|issue=3|pages=190–203|doi=10.1002/anie.198701901}}</ref> Carbonyl groups are also known to direct the hydrogenation by the Crabtree catalyst to be highly regioselective.<ref>{{cite journal|last1=Schultz|first1=A.|last2=McCloskey|first2=P.|date=1985|title=Carboxamide and carbalkoxy group directed stereoselective iridium-catalyzed homogeneous olefin hydrogenations|journal=]|volume=50|issue=26|pages=5905–5907|doi=10.1021/jo00350a105}}</ref><ref>{{cite journal|title = Directing effects in homogeneous hydrogenation with PF6|last1=Crabtree|first1=R. H.|last2=Davis|first2= M. W. | journal = J. Org. Chem. | date = 1986 | volume = 51 | issue = 14 | pages = 2655–2661|doi = 10.1021/jo00364a007}}</ref><ref>{{cite journal|last1=Crabtree|first1=R.|last2=Davis|first2=M.|date=1983|title=Occurrence and origin of a pronounced directing effect of a hydroxyl group in hydrogenation with PF<sub>6</sub>|journal=Organometallics|volume=2|issue=5|pages=681–682|doi=10.1021/om00077a019}}</ref>
		⚫	:]
			The directing effect that causes the stereoselectivity of hydrogenation of terpen-4-ol with Crabtree’s catalyst is shown below.
			]
			== History==
		⚫	Crabtree and graduate student George Morris discovered this catalyst in the 1970s while working on iridium analogues of ] ]-based catalyst at the ] at ], near Paris.
			Previous ] catalysts included Wilkinson’s catalyst and a cationic rhodium(I) complex with two ] groups developed by Osborn and Schrock.<ref>{{cite journal|last1=Schrock|first1=R.|last2=Osborn|first2=J. A.|date=1976|title=Catalytic hydrogenation using cationic rhodium complexes. I. Evolution of the catalytic system and the hydrogenation of olefins.|journal=Journal of the American Chemical Society|volume=98|issue=8|pages=2134–2143|doi=10.1021/ja00424a020}}</ref> These catalysts accomplished hydrogenation through displacement; after hydrogen addition across the metal, a solvent or a phosphine group dissociated from the rhodium metal so the olefin to be hydrogenated could gain access to the active site.<ref name ="original"/> This displacement occurs quickly for rhodium complexes but occurs barely at all for iridium complexes.<ref>{{cite journal|last1=Osborn|first1=J.|last2=Shapley|first2=J.|date=1970|title=Rapid intramolecular rearrangements in pentacoordinate transition metal compounds. Rearrangement mechanism of some fluxional iridium(I) complexes|journal=Journal of the American Chemical Society|volume=92|issue=23|pages=6976–6978|doi=10.1021/ja00726a047}}</ref> Because of this, research at the time focused on rhodium compounds instead of compounds involving transition metals of the third row, like iridium. Wilkinson, Osborn, and Schrock also only used coordinating solvents.<ref>{{cite journal|last1=Young|first1=J.|last2=Wilkinson|first2=G.|date=1966|title=The preparation and properties of tris(triphenylphosphine)halogenorhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives.|journal=J. Chem. Soc. A|volume=1966|page=1711|doi=10.1039/J19660001711}}</ref>
			Crabtree noted that the ligand dissociation step does not occur in ], and so posited that this step was limiting in homogeneous systems.<ref name="original" /> They sought catalysts with "irreversibly created active sites in a noncoordinating solvent." This led to the development of the Crabtree catalyst, and use of the solvent CH<sub>2</sub>Cl<sub>2</sub>.
	==References==		==References==
			{{reflist|30em}}
	<references/>
	{{Iridium compounds}}		{{Iridium compounds}}
	]		]
	]		]
	]		]
	]		]
			]
			]
	]
	]
	]
	]